Urinary bladder

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Urinary bladder
Urinary system.svg
1. Human urinary system: 2. Kidney, 3. Renal pelvis, 4. Ureter, 5. Urinary bladder, 6. Urethra. (Left side with frontal section)
7. Adrenal gland
Vessels: 8. Renal artery and vein, 9. Inferior vena cava, 10. Abdominal aorta, 11. Common iliac artery and vein
With transparency: 12. Liver, 13. Large intestine, 14. Pelvis
2605 The Bladder.jpg
Female bladder (visible due to lack of prostate), showing transitional epithelium as well as part of the wall in a histological cut-out.
Latin vesica urinaria
Gray's [1]
System Urinary system
Artery Superior vesical artery
Inferior vesical artery
Umbilical artery
Vaginal artery
Vein Vesical venous plexus
Nerve Vesical nervous plexus
Precursor urogenital sinus
MeSH Bladder
Dorlands
/Elsevier
Urinary bladder
Anatomical terminology

The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow[1] muscular, and distensible (or elastic) organ, the bladder sits on the pelvic floor. Urine enters the bladder via the ureters and exits via the urethra. It's almost impossible to give an exact measurement for the volume of the human bladder, but different sources mention 500 mL (~17 oz) to 1000 mL (~34 oz).[2]

Structure[edit]

Detrusor muscle[edit]

The detrusor muscle is a layer of the urinary bladder wall made of smooth muscle fibers arranged in spiral, longitudinal, and circular bundles. When the bladder is stretched, this signals the parasympathetic nervous system to contract the detrusor muscle. This encourages the bladder to expel urine through the urethra. A meta-analysis on the effect of voiding position on urodynamics in males found that sitting down allows for improved contraction of the detrusor muscle.[3]

Fundus[edit]

The fundus of the bladder is the base of the bladder, formed by the posterior wall. It is lymphatically drained by the external iliac lymph nodes. The peritoneum lies superior to the fundus.

Innervation[edit]

The bladder receives motor innervation from both sympathetic fibers, most of which arise from the hypogastric plexuses and nerves, and parasympathetic fibers, which come from the pelvic splanchnic nerves and the inferior hypogastric plexus.[4]

Sensation from the bladder is transmitted to the central nervous system (CNS) via general visceral afferent fibers (GVA). GVA fibers on the superior surface follow the course of the sympathetic efferent nerves back to the CNS, while GVA fibers on the inferior portion of the bladder follow the course of the parasympathetic efferents.[4]

For the urine to exit the bladder, both the autonomically controlled internal sphincter and the voluntarily controlled external sphincter must be opened. Problems with these muscles can lead to incontinence.[5]

Histology[edit]

Since the urinary bladder has a transitional epithelium, it does not produce mucus.[6]

Development[edit]

The human urinary bladder is derived in embryo from the urogenital sinus and, it is initially continuous with the allantois. In males, the base of the bladder lies between the rectum and the pubic symphysis. It is superior to the prostate, and separated from the rectum by the rectovesical excavation. In females, the bladder sits inferior to the uterus and anterior to the vagina; thus, its maximum capacity is lower than in males. It is separated from the uterus by the vesicouterine excavation. In infants and young children, the urinary bladder is in the abdomen even when empty.[7]

In other animals[edit]

Bladders occur throughout much of the animal kingdom, but are very diverse in form[further explanation needed] and in some cases are not homologous with the urinary bladder in humans.[citation needed]

Function[edit]

Main article: Urination

The urinary bladder usually holds 300-350 ml of urine. As urine accumulates, the rugae flatten and the wall of the bladder thins as it stretches, allowing the bladder to store larger amounts of urine without a significant rise in internal pressure.[8]

Frequent urination can be due to excessive urine production, small bladder capacity, irritability or incomplete emptying. Males with an enlarged prostate urinate more frequently. One definition of overactive bladder is when a person urinates more than eight times per day,[9] though there can be other causes of urination frequency.[citation needed] Though both urinary frequency and volumes have been shown to have a circadian rhythm, meaning day and night cycles,[10] it is not entirely clear how these are disturbed in the overactive bladder.

Clinical significance[edit]

Disorders[edit]

A diverticulum of the bladder

Disorders of or related to the bladder include:

Additional images[edit]

See also[edit]

References[edit]

  1. ^ Howard A. Werman, Keith J. Karren.[full citation needed]
  2. ^ Volume of a Human Bladder
  3. ^ de Jong, Y; Pinckaers, JH; Ten Brinck, RM; Lycklama À Nijeholt, AA; Dekkers, OM (2014). "Urinating Standing versus Sitting: Position Is of Influence in Men with Prostate Enlargement. A Systematic Review and Meta-Analysis.". PloS one 9 (7): e101320. doi:10.1371/journal.pone.0101320. PMID 25051345. 
  4. ^ a b Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. pp. 227–228. ISBN 0-7817-6274-X. 
  5. ^ "Urinary Incontinence - Causes". NHS. Retrieved 2013-08-21. 
  6. ^ Chin T, Liu , Tsai H, Wei C (September 2007). "Vaginal reconstruction using urinary bladder flap in a patient with cloacal malformation". Journal of Pediatric Surgery 42 (9): 1612–5. doi:10.1016/j.jpedsurg.2007.04.040. PMID 17848259. 
  7. ^ Moore, Keith L.; Dalley, Arthur F (2006). Clinically Oriented Anatomy (5th ed.). Lippincott Williams & Wilkins. 
  8. ^ Marieb, Mallatt. "23". Human Anatomy (5th ed.). Pearson International. p. 700. 
  9. ^ "Overactive Bladder". Cornell Medical College. Retrieved 2013-08-21. 
  10. ^ Negoro, Hiromitsu (2012). Involvement of urinary bladder Connexin43 and the circadian clock in coordination of diurnal micturition rhythm. doi:10.1038/ncomms1812. 

External links[edit]